Cathode-ceramic assembly for electron guns and method of making



April 1963 R. w. OSBORNE EI'AL 3,087,082

CATHODE-CERAMIC ASSEMBLY FOR ELECTRON GUNS AND METHOD OF MAKING Filed Feb. 9, 1960 INVENTORS Richard \M Osborne t Thomas J. Morris by MW was! 3 087,082 CATHODE-CERAMIL ASSEMBLY Fill ELECTRON GUNS AND METHOD OF MAG Richard W. Osborne, Marion, and Thomas J. Morris, Gas City, Ind, assignors to Radio Corporation of America,

a corporation of Delaware Filed Feb. 9, 1960, Ser. No. 7,597 11 Claims. (Cl. 313-337) This invention relates to electron guns such as are used in cathode ray tubes and particularly to an improved assembly of a cathode and a ceramic wafer cathode support for such guns and a method of making such an assembly.

One kind of conventional electron gun used in cathode ray tubes includes a plurality of electrodes mounted in axially spaced relation. Usually one of the electrodes serves as a control grid and takes the form of a cup having a central aperture in the end wall thereof. A centrally apertured ceramic wafer is mounted within the grid cup parallel to the apertured end wall of the cup. A tubular cathode sleeve having one end thereof closed and coated with emissive material is mounted through the aperture of the ceramic wafer concentrically within the grid cup with its coated end adjacent the cup aperture. For the sake of brevity, the assembly of the cathode sleeve and the apertured ceramic wafer will herein be referred to simply as a cathode-ceramic assembly.

One arrangement for securing the cathode sleeve within the aperture of the ceramic wafer in such assemblies has been by crimping of the cathode sleeve. A pair of circumferential outwardly extending flanges in the form of flattened gathers or crimps are provided around the cathode sleeve which bear against the flat faces of the ceramic wafer. Such prior art assemblies have resulted in problems of microphonics and undesirable cathode operating temperature characteristics such as poor operating temperature uniformity from assembly to assembly.

It is therefore an object of our invention to provide an improved cathode-ceramic assembly and method of fabricating such an assembly which provides reduced microphonics and good temperature operation uniformity from assembly to assembly.

Another object of our invention is to provide an improved cathode-ceramic assembly having the characteristics mentioned in the preceding object in which the assembly and method of fabrication thereof is simple, economical, uses industry standardized cathode and ceramic parts, and which can be fabricated using conventional tools, the operation of which does not require highly skilled labor.

Another object of our invention is to provide an improved cathode-ceramic assembly and method of fabrication thereof which can be easily varied to provide a selected operating temperature characteristic of the cathode.

Briefly, according to our invention, after a cathode sleeve has been crimped tightly against the flat faces of an apertured ceramic wafer it is provided with a circumferentially-uniform, outward radial bulge between the flange crimps thereof, preferably into contact with the aperture wall of the ceramic. Such a bulge according to our invention is herein termed a post-crimp-bulge, i.e.,

it is provided after the crimping of the cathode sleeve is completed.

In the drawings:

walled, circular, central aperture.

3,087,082 Patented Apr. 23, 1963 double crimped cathode-ceramic assembly referred to above, and

FIG. 2 is a section view with parts broken away of a cathode-ceramic assembly according to our invention together with one suitable tool for providing the post-crimp bulge in the cathode sleeve according to the invention.

In FIG. 1 a conventional, prior, art, double crimped cathode-ceramic assembly 8 is shown to comprise an apertured ceramic wafer 10 and a tubular cathode sleeve 12. The cathode sleeve 12 is mounted through the aperture of the ceramic wafer 10 and held therein by a pair of circumferential flanges 14 crimped in the sleeve 12 which are pressed against the opposite flat faces 16 of the ceramic wafer 10.

According to well-known fabrication techniques, such a cathode-ceramic assembly 8, as shown in FIG. 1, is made by first providing one of the circumferential crimps 14 in the cathode sleeve 12. The sleeve 12 is then inserted in the aperture of the ceramic wafer 10 and the one crimp 14 caused to rest against one face of the wafer 10. The other crimp 14 is then made in the cathode sleeve 12 and pressed against the opposite face of the ceramic wafer. The two crimps 14 may be made by any-well-known technique such as by use of a split expander tool to provide a pair of bulges in the cathode sleeve 12 which are subsequently flattened to form the crimps 14 as illustrated. Alternatively, it is known to provide securing flanges on the sleeve 12 other than by crimps.

The conventional cathode-ceramic assembly 8 of FIG. 1 has proved to he basically a desirable assembly for a number of reasons. Among such reasons is the fact that such an assembly comprises only two parts, thus contributing to an economical and easily assembled structure. Moreover, the ceramic wafer 10 has only simple contours which also contributes to economy. For example, the ceramic wafer 10 is provided with a simple, straight- Also, the method of holding the cathode sleeve 12 in the ceramic wafer 10, viz., by a pair of circumferential crimps, entails relatively low cost processing techniques. For these reasons, among others, the cathode-ceramic assembly 8 of FIG. 1 has found extensive use in the industry.

However, the cathode-ceramic assembly 8 frequently results in a microphonic structure due to a loosening of the parts thereof when the cathode sleeve 12 is raised to operating temperature. When raised to operating temperatures, the cathode sleeve 12, being metallic, expands much more than does the ceramic wafer 10. Axial expansion of the cathode sleeve 12 results in the two circumferential crimps 14 moving farther apart and away from the surfaces 16 of the ceramic wafer 10. Since the cathode sleeve 12 is provided as a loose. fit in the aperture of the ceramic wafer 10, such expansion results in loosening the firm mounting of the cathode sleeve 12 in the ceramic wafer 10. Accordingly, microphonics may occur in the electron tube into which the assembly is incorporated.

Another undesirable characteristic of the cathodeceramic assembly 8 is nonuniformity of cathode operating temperature from assembly to assembly. Ideally, the contact between the cathode 12 and the ceramic 10 is made essentially only by the crimps 14 against the surfaces 16 of the ceramic. The area of contact of these crimps can be closely controlled and uniformly reproduced from assembly to assembly. However, it has been discovered that oftentimes during fabrication of such an assembly--most likely during the flattening of the final crimp of the cathode-a bulge is sometimes accidentially produced in the cathode sleeve 12 between the two crimps 14 which may contact the aperture wall 18 of the ceramic wafer 10. However, occurrence of such a condition is not easily controllable according to conventional fabrication techniques and, accordingly, such contacting bulges occur randomly. Moreover, since such bulges are not provided uniformly around the cathode sleeve and against the aperture wall 18, they provide no reliable added support for the cathode 12 within the ceramic wafer 12, such as would contribute to a lessening of microphonic difiiculties.

However, as is well known, the greater contact between the cathode sleeve 12 and the ceramic wafer 10, the greater the heat loss from the cathode 12 due to thermal conductivity from the cathode 12 to the ceramic wafer 10. Accordingly, for a given heat input by virtue of a given heater coil and power consumption thereby, the operating temperature of the cathode 12 will vary inversely according to the contact between the cathode sleeve 12 and the ceramic wafer 10. Thus, in order to obtain uniform operating temperature characteristics from assembly to assembly it is necessary to obtain uniform contact from assembly to assembly. But the prior art has neither obtained such uniform contact in the cathode ceramic assembly 8 of FIG. 1 nor appreciated why this assembly failed to give such uniform temperature characteristics.

FIG. 2 shows a completely fabricated cathode-ceramic assembly 28 according to our invention. The assembly 28 comprises a conventional ceramic wafer and a cathode sleeve 30 similar to the sleeve 12 of FIG. 1. As in the case of the cathode-ceramic assembly 8 of FIG. 1, the assembly 28 is fabricated by first providing a circumferential crimped flange 32 in a straight-walled metal sleeve. The singly crimped cathode sleeve 31} is then inserted into the aperture of the ceramic wafer 10 and the crimp 32 is brought into contact with one fiat face 34 of the ceramic wafer 10. The cathode sleeve 30 is then provided with a bulge adjacent the other flat face 36 of the ceramic wafer and the bulge then flattened into a second circumferential crimped flange 37 and pressed against the face 36 of the ceramic wafer 10'. At this stage of fabrication, the cathode-ceramic assembly 28 is similar to the cathode-ceramic assembly 8 of FIG. 1.

With the cathode sleeve 30 thus crimped tightly against both flat faces 34 and 36 of the ceramic wafer 10, a cir cumfere'ntially-uniform, outward radial post-crimp-bulge 38 is provided in the cathode sleeve 30 between the two crimps 32 and 37.

The post-c'rimp-bulge 38 is preferably made to contact the aperture wall 40 of the ceramic wafer. However, this is not essential. As hereinafter more fully described, the occurrence of loosened cathode-ceramic assemblies due to thermal expansion is lessened simply by a post-crimpexpander tool 42 suitable for providing the post-crimp outwardradialbulge in the cathode sleeve. The expander tool 42 includes a tubular member 44 having a rounded fiat head 46 on one end thereof. The tubular member 44 is axially split along three radii spaced 120 from each other. The axial splits extend from the head 46 back along the tubular member 44 a predetermined distance.

The axial bore of the tubular member 44 tapers from a given diameter to a smaller diameter in the direction towardthe head 46 in the region of the axial splits therein. A tapered center plunger 48 is provided which, when adraised to operating temperatures.

4,. vanced axially toward the head 46, causes the three sections of the head 46 to be moved radially outward. Such action of the head 46 is used to uniformly effect an outward radial bulging of the cathode sleeve.

in the case where the post-crimp-bulge 38 is provided by the split expander tool 42, the bulge 38 will include three bulged portions spaced circumferentially from each other. If desired, a circumferentially continuous bulge can be easily provided by use of other Well-known bulging tools and techniques such as by expansion of a rubber O-ring.

According to our invention a number of advantages are provided by the post-crimp-bulging of the cathode sleeve 30. Foremost is the reduction of possible microphonics of an electron tube into which the cathodeceramic assembly 28 may be incorporated. By virtue of the contact between the post-crimp-bulge 38 and the ceramic aperture wall 40, added contact is provided between the cathode sleeve 30 and the ceramic wafer 10. Thus, an even firmer mounting of the cathode sleeve 30 within the ceramic wafer 10 results. Moreover, when the cathode sleeve 30 is raised to operating temperatures, the post-crimp-bulge 38 bears even more tightly against the aperture wall 40 of the ceramic wafer 10'.

A second very important characteristic of the cathode ceramic assembly 28 by which microphonics in the tube is avoided lies in the fact that the radial post-crimp-bulge 38 is provided after the cathode sleeve 30 has been firmly crimped against the ceramic surfaces 34 and 36. The effect of such post-crimp-bulging is that the cathode sleeve 30, in being bulged between the two completed crimps 32 and 37, is placed in axial tension throughout that region. Accordingly, when the cathode sleeve 30 is raised to operating temperatures, the axial tension resulting from the post-crimp-bulging must first be relieved before the crimps 32 .and 37 can expand axially out of contact with the ceramic surfaces 34 and 36. Our experience has been that the usual operating temperature of a cathode is not sufficient to relieve this tension and substantially expand the crimps 32 and 37 out of contact with the ceramic surfaces 34 and 36.

Extensive testing has proved that even where the postcrimp-bulge is not radially extended suflicient to firmly contact the aperture wall 40, the cathode sleeve 30 still remains tightly fixed in the ceramic wafer 10 when it is This demonstrates the advantageous effect of axially tensioning the cathode sleeve in the region between the two circumferential crimps 32 .and 37.

Insofar as reduction of microphonics is concerned, the post-crimp-bulge 38 can be of any desired radius. A large radius of bulge, as might be provided by a large radius of expanding tool head 46, merely results in 'providing greater contact between the post-crimp-bulge 38 and the aperture wall 40. As hereinbefore explained, the greater the cathode-ceramic contact, the greater the heat conduction from the cathode, and the lower the resultant cathode operating temperature. However, for the purpose of providing a selected high cathode temperature operating characteristic, it may be desired to provide a small radius bulge 38 and thereby provide a small area of contact between the cathode .sleeve 30 and the ceramic wafer 10. Selection of bulge radius will therefore be influenced by the particular cathode temperature operating characteristics desired in any particular application.

As hereinbefore stated, prior art fabrication technique of the cathode ceramic assembly 8 of FIG. 1 occasion- .ally resulted in an outward radial bulge between the circumferential crimps 14 of the cathode sleeve 12. However, as has been also stated, due to the nonuniform occurrence of such bulges from assembly to assembly, their ocurrence was in fact objectionable rather than useful. Moreover, such accidental bulging by prior art techniques was the result of axially compressing the cathode sleeve during the crimp pressing step to thereby provide a resultant bulge. Thus, the advantage of axial tension of the cathode sleeve was not even accidentally present in the sleeve 12. Contrary to such prior art accidental bulging, post-crimp-bulging according to our invention provides not only the desired uniformity but also an axial tensioning of the cathode sleeve rather than an axial compressing of the sleeve.

For similar reasons any attempt to provide a press fit of a cathode sleeve into an apertured ceramic wafer by providing a suitably sized cathode sleeve, fails to provide a tensioned characteristic of the sleeve between the circumferential crimps subsequently provided therein. In such a press fit type cathode-ceramic assembly, if the contact area between the crimps is great enough, for example throughout the thickness of the ceramic wafer, to provide secure assemblies when the crimps have thermally expanded out of contact with the ceramic wafer, then the contact is so great that it also results in a low temperature cathode operation. If the press-fit contact is made suitably small, then when the crimps expand away from the ceramic surfaces due to normal operational heating the contact is also so small that it permits a possible rocking of the cathode sleeve in the ceramic. Moreover, if the cathode sleeve is crimped after the desired cathode-ceramic contact is established by the abovementioned press fit, such contact is disturbed or even destroyed because the sleeve oftentimes wrinkles in the region between the two crimps during the crimping operation. Also, when a press fit cathode-ceramic assembly is attempted, high-scrap production results due to chipped ceramic parts. For these reasons a press fit cathodeceramic assembly has failed to find acceptance in the industry.

Post-crimp-bulging according to our invention provides, among others, the following advantages not all of which are present in any of the known prior art fabrication techniques: (a) a radially bulged contact between the cathode sleeve and the aperture wall of the ceramic to aid in providing a firm support of the cathode within the ceramic wafer, (b) axial tensioning of the cathode sleeve in the region between the two circumferential crimps to reduce or prevent within certain thermal limits the thermal expansion of the cathode sleeve and thereby reduce or prevent the resulting loss of contact between the crimps and the ceramic wafer, no tendency to distort or otherwise loosen contact between the cathode sleeve and the aperture wall in the ceramic because of a crimping fabrication step subsequent to the establishing of the cathode ceramic contact, (d) ease of providing selective cathode temperature operating characteristics by selection of the radius of the postcrimp-bulge, (e) the ability to obtain circumferential uniformity of bulge within a given cathode-ceramic assembly and reproducible uniformity from assembly to assembly, and (f) the realization of advantages (a) through (e) with the use of simple, industry standardized, economical parts and processing techniques.

One preferred cathode-ceramic assembly 28, which has found extensive commercial success, is dimensioned as follows:

Mils Ceramic wafer diameter 370 Ceramic wafer aperture diameter 128 Ceramic wafer thickness 84 Cathode diameter 124 Cathode wall thickness 4 Cathode crimp outer diameter 160 Radius of post-crim-p-bulge 1520 We claim:

1. The method of fabricating a cathode-ceramic assembly comprising the steps of securing a cylindrical metal sleeve within the aperture of an apertured ceramic wafer by a pair of axially spaced circumferential flanges extending from said sleeve and disposed against the flat v 6 faces of said wafer around the aperture therein, and then bulging said sleeve radially outward in the region thereof between said flanges and into contact with said wafer.

2. The method of fabricating a cathode-ceramic assembly comprising the steps of providing a first circumferential flange around a cylindrical cathode sleeve, inserting said sleeve into the aperture of an apertured ceramic wafer so that said flange contacts oneflat face of said wafer around said aperture, securing said sleeve within said wafer by providing a second circumferential flange around said sleeve and against the other flat face of said wafer surrounding said aperture, and then bulging said cathode sleeve radially outward in the region thereof between said flanges and into contact with said wafer.

3. The method of fabricating a cathode-ceramic assembly comprising the steps of providing a circumferential crimp in a cathode sleeve, inserting said sleeve into the aperture of an apertured ceramic wafer so that said crimp contacts one flat face of said wafer around said aperture, said aperture being slightly greater in diameter than the diameter of said sleeve, circumferentially crimping said sleeve against the other flat face of said wafer surrounding said aperture to fix said sleeve in said wafer, and then bulging said cathode sleeve radially outward in the region thereof between said crimps.

4. The method of preventing loosening due to thermal expansion of a cathode-ceramic assembly having a cathode sleeve fixed in the aperture of an apertured ceramic Wafer by a pair of circumferential crimps contacting the flat faces of said wafer comprising the step of post-crimpbulging the cathode sleeve thereof between its circumferential flanges.

5. The method of preventing thermal expansion from loosening the cathode sleeve within the ceramic wafer in an assembly having a cathode sleeve fixed in the aperture of an apertured ceramic wafer by a pair of circumferential flanges contacting the flat faces of said wafer comprising the step of circumferentially uniformly bulging said sleeve radially outward between the flanges thereof.

6. The method of preventing an assembly having a cathode sleeve fixed in the aperture of an apertured ceramic wafer by a pair of circumferential crimps from loosening due to thermal expansion of the cathode sleeve within the ceramic wafer comprising the step of bulging said sleeve radially outward in the region between the crimps thereof after said crimps have been made.

7. In a double-crimped, cathode-ceramic assembly having a cathode sleeve fixed in the aperture of an apertured ceramic wafer by a pair of circumferential crimps, the method of preventing the cathode sleeve from loosening in the ceramic wafer due to thermal expansion of the assembly, comprising the step of axially tensioning the cathode sleeve between the two circumferential crimps thereof after said crimps have been made.

8. A cathode-ceramic assembly comprising a ceramic wafer having an aperture therethrough, a cathode sleeve disposed through said aperture and locked in said wafer by a pair of circumferential crimped flanges, said cathode sleeve being axially tensioned between said flanges by a radial bulge between said flanges.

9. A cathode-ceramic assembly comprising a ceramic wafer having an aperture therethrough, a cathode sleeve disposed through said aperture and secured within said wafer by a pair of circumferential flanges contacting the flat faces of said wafer around said aperture, said cathode sleeve being substantially circumferentially uniformly post-crimp bulged radially outwardly between said flanges into contact with said ceramic to axially tension said sleeve between said flanges.

10. A cathode-ceramic assembly for an electron gun comprising a ceramic wafer having an aperture therein, a tubular metal sleeve mounted coaxially in said aperture and secured therein by a pair of circumferential 7 flanges extending from said sleeve and bearingon the flat faces of said wafer around said aperture, said sleeve being axially t'ensioned between said flanges.

11. A cathode-ceramic assembly for an electron gun comprising a ceramic wafer having an aperture therein, a tubular metal sleeve mounted coaxially in said aperture and secured therein by a pair of circumferential crimped flanges in said sleeve bearing on the flat faces of said wafer around said aperture, said sleeve having a postcrimp-bulge therein between said erimped flanges.

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS Great Britain Dec. 19, 1956 Germany Jan. 31, 1957 

9. A CATHODE-CERAMIC ASSEMBLY COMPRISING A CERAMIC WAFER HAVING AN APERTURE THERETHROUGH, A CATHODE SLEEVE DISPOSED THROUGH SAID APERTURE AND SECURED WITHIN SAID WAFER BY A PAIR OF CIRCUMFERENTIAL FLANGES CONTACTING THE FLAT FACES OF SAID WAFER AROUND SAID APERTURE, SAID CATHODE SLEEVE BEING SUBSTANTIALLY CIRCUMFERENTIALLY UNIFORMLY 